HERSCHELOBSERVATIONS OF EXTRAORDINARY SOURCES: ANALYSIS OF THE FULLHERSCHEL/HIFI MOLECULAR LINE SURVEY OF SAGITTARIUS B2(N)

Abstract

A sensitive broadband molecular line survey of the Sagittarius B2(N) star-forming region has been obtained with the HIFI instrument on the Herschel Space Observatory, offering the first high-spectral resolution look at this well-studied source in a wavelength region largely inaccessible from the ground (625-157 µm). From the roughly 8,000 spectral features in the survey, a total of 72 isotopologues arising from 44 different molecules have been identified, ranging from light hydrides to complex organics, and arising from a variety of environments from cold and diffuse to hot and dense gas. We present an LTE model to the spectral signatures of each molecule, constraining the source sizes for hot core species with complementary SMA interferometric observations, and assuming that molecules with related functional group composition are cospatial. For each molecule, a single model is given to fit all of the emission and absorption features of that species across the entire 480-1910 GHz spectral range, accounting for multiple temperature and velocity components when needed to describe the spectrum. As with other HIFI surveys toward massive star forming regions, methanol is found to contribute more integrated line intensity to the spectrum than any other species. We discuss the molecular abundances derived for the hot core, where the local thermodynamic equilibrium approximation is generally found to describe the spectrum well, in comparison to abundances derived for the same molecules in the Orion KL region from a similar HIFI survey. Notably, we find significantly higher abundances of amine-and amide-bearing molecules (CH 3 NH 2 , CH 2 NH, and NH 2 CHO) toward Sgr B2(N) than Orion KL, and lower abundances of some complex oxygen-bearing molecules (CH 3 OCHO in particular). In addition to information on the chemical composition of the hot core, the strong far-IR dust continuum allows a number of molecules to be detected in absorption in the Sgr B2(N) envelope for the first time at high spectral resolution, and we discuss the possible physical origin of the kinematic components observed in absorption. Additionally, from the detection of new HOCO + transitions in absorption compared to published HCO + isotopic observations, we -2discuss constraints on the gas-phase CO 2 abundance and compare this to observations of the ice composition in the Galactic Center region, and to CO 2 abundance estimates toward other highmass star-forming regions. The reduced HIFI spectral scan and LTE model are made available to the public as a resource for future investigations of star forming regions in the submillimeter and far-infrared. * Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

CO, Water, and Tentative Methanol in η Carinae Approaching Periastron

“…Even at the modest level of excitation of the J = 10 − 9 line, the association of methanol with the absorption is also most plausible. Methanol absorption lines with higher upper level energies have been observed in other environments, such as the J = 5 − 5 K = 5 − 4 E-type torsional lines (E u = 171.9 K) observed towards Sgr B2(N) in both emission and significant absorption, tracing warm and very cool (T ≤ 10 K) gas clouds (Neill et al 2014). We also note the ALMA detection of the ground and first excited states of HCN and H 13 CN J − 4 − 3 lines in absorption toward the central star in η Car, where the ν 2 = 1 state has an energy of 1050 K, indicating unusually excited conditions close to the binary (Bordiu & Rizzo 2019).…”

Rotational spectral studies of O(1D) insertion reactions with methane and ethylene: Methanol and vinyl alcohol in a supersonic expansion

“…However, this detection has not been confirmed at higher frequencies [59,60]. Higher-frequency spectroscopic measurements that extend beyond the work of [57] would aid future astronomical searches for this molecule.…”

eXtended CASA Line Analysis Software Suite (XCLASS)

“…The XCLASS interface for CASA contains the myXCLASS program, originally developed by P. Schilke (Schilke et al 2001;Comito et al 2005;Zernickel et al 2012;Crockett et al 2014a,b;Neill et al 2014) based on the GILDAS 11 package CLASS, which models a spectrum by solving the radiative transfer equation for an isothermal object in one dimension, the detection equation (Stahler & Palla 2005). Here, LTE is assumed, that is, the source function is given by the Planck function of an excitation temperature, which does not need to be the physical temperature, but is constant for all transitions.…”

“…The toolbox described in this paper offers not only the possibility to model data by using the myXCLASS program (Schilke et al 2001;Comito et al 2005;Zernickel et al 2012;Crockett et al 2014a,b;Neill et al 2014), which computes synthetic spectra by solving the detection equation similar to software packages like Weeds (Maret et al 2011) and CASSIS 1 , but also makes use of the optimization package MAGIX (Möller et al 2013). MAGIX provides a framework of an easy interface between existing codes and an iterating engine that attempts to minimize deviations of the model results from available observational data, constraining the values of the model parameters and providing corresponding error estimates.…”